Capsaicin is the major pungent principle of hot peppers from the plant genus Capsicum, the members of which are used extensively in foods, both for their coloring properties and their pungency. Peppers have been accredited with healing properties by practitioners of folk lore medicine, worldwide. However, in recent years these claims have been scientifically validated. The "fire" and "heat" of capsaicin is now used to provide pain relief in a number of situations.

Intrigued by the customary practice of feeding peppers to Hungarian children, pharmacologist Nicholas Jancso began extensive studies on the biological effects of capsaicin, in 1940, providing valuable guidelines for its use as a therapeutic agent. Capsaicin is classified by the US FDA as a counter-irritant, a substance which may be deliberately applied to the skin to relieve more serious symptoms such as inflammation and pain. It is recommended that creams containing capsaicin, (0.025% to 0.075%) be applied 3-4 times daily since a burning sensation may develop if it is used less frequently. The efficacy of topical preparations of capsaicin, therefore, depends more or less upon continuous use.

Although the precise mechanism of action of capsaicin is not fully understood, current evidence suggests that capsaicin renders the applied area insensitive to pain by depleting Substance P, a neurotransmitter which transmits pain impulses from the peripheral neurons to the central nervous system. The name "Substance P" was given by Ulf S. von Euler, where P stands for pain. It is during this process of high speed depletion that the initial irritation is experienced, when capsaicin is applied. Pain relief is experienced after Substance P is totally depleted.

Capsaicin has also been demonstrated to enhance energy metabolism in mammals, inducing thermogenesis. It has also been shown to reduce the levels of serum cholesterol and promote hair growth in experimental models. Preparations containing capsaicin have been formulated for topical applications to provide temporary warming pain relief for minor aches and pains of muscles and joints associated with arthritis, simple backache, strains, sprains, psoriasis and post-operative neuralgia.

The FDA has approved the use of capsaicin at levels ranging from 0.025% to 0.25% for therapeutic applications.